theres 1 vote lol
Looks a little like a Logie's vote grab though

5000 years is a long time before electric kettles ... the local hotsprings do have hot water and this may be where the tradition began. the thoughts of drinking sulfur water disturbs me. 

 biggest problem of sulfur in drinking water is that it stinks. Like other minerals, sulfur can leave stains in plumbing fixtures such as sinks and toilets. Clothing washed in water that is high in sulfur may also become stained. Water that contains as little as one part per million of hydrogen sulfide can tarnish copper and silver. 

The bacteria that produce hydrogen sulfide gas produce slime, which can be white, gray or black. These sulfur bacteria can create conditions favorable to other bacteria, including iron bacteria, in which case you might see a reddish-brown slime. Any of those slimes will coat plumbing pipes, which will cause clogs and lead to corrosion.

 sulfur in drinking water can contribute to diarrhea, which leads to dehydration.

small wonder why shitting anywhere is ok, it's the water. and trust me, the stain in your fancy western toilet is, you guessed it, sulfur.

I do keep a hot water cooker running all the time and had to switch to filtered water for heating. I tried to use the tap water but the stainless steel liner in the cooker would be a yellow color in about 4 days. I would have to use white vinegar to clean the damn thing and start again. So now I boil filtered water for everything.

Sucking hotwater